The Sadness

Medical experts and government officials in Taiwan argue over the "Alvin virus", a virus responsible for an infection similar to influenza. The virologists warns that the virus would mutate, but the government, prioritizing their efforts for a re-election, responds by downplaying the viral threat, while most of the general public expresses skepticism. Jim and his girlfriend and Kat are preparing for their usual day in an apartment complex in Taipei when he spots an elderly woman covered in blood on a nearby roof but disappears when he looks away.

As Jim drives Kat to the train station, they pass by an ambulance with a corpse on the stretcher. After dropping her off, he stops by at a cafe when the same elderly woman appears and spits a thick mucus on one of the customers, who then turns on and kills other nearby patrons. The elderly woman was then run over by an infected driver, and Jim flees back to his home, chased by an infected mob. His infected neighbor arrives and cuts off his fingers using his pruning shears, forcing Jim to flee once more.

Inside a subway train, Kat offers a seat to a stranger named Molly when they witness an infected man stabbing indiscriminately, killing and infecting several other passengers. One of the infected is a pervy businessman who stabs Molly in the eye using his umbrella. Kat drags an injured Molly out of the station, while being pursued by the businessman who decapitates a bystander with an axe attempting to defend the two. They barely manage to escape as the subway employee, Kevin, closes the door shutter on them, who Molly subsequently punches. Kat, Molly and Kevin reach a hospital – filled with weary survivors and police officers – to patch Molly's eye and Kevin's bloodied nose. They then witnesses the president being blown up by an infected army general with a grenade during his televised address, triggering a brawl from those unsympathetic to the president's death. The businessman then kills the officer amidst the chaos and rapes Molly, infecting her with the virus. When Kevin is spotted by her, the infected horde held him down while Molly savagely kills him using the bone saw.

Jim contacts Kat, telling her to stay where she is while he tries to reach her. Kat repeatedly bludgeons the businessman to death with the fire extinguisher, just as she is spotted by Alan Wong, one of the doctors who tried to warn the public of the Alvin virus. Wong explains to Kat that the virus hijacks the limbic system of the brain, creating an irresistible and aggressive desire to act out their most violent, sadistic impulses while retaining their intelligence and speech. Wong injects Kat with the Alvin virus, revealing that he is conducting human trials by injecting the virus on newborn infants in a bid to discover an antibody for the virus. When Wong finds that Kat is seemingly immune, he escorts her to the roof where a helicopter is on their way to evacuate them.

Jim arrives at the hospital, revealing that he was already infected with the Alvin virus. Wong shoots Jim in the neck, but the gun misfires at the second shot and Jim strikes an axe at his neck, Wong, who was also infected prior to their encounter, expresses to Jim in his dying breath that he enjoyed euthanizing the infected infants. Kat flees and locks the metal gate, separating Jim and the stairwell that leads to the roof. Despite knowing that he is infected, Kat tries to persuade Jim. However, Jim, also dying from his injuries, says that while he loves her, the virus has given him purpose, and that he intends to torture and kill her. Kat laughs hysterically before she leaves him behind to a sound of an approaching helicopter. The fate of Kat is unknown as the camera pans to a lifeless Jim with a deathly grin on his face as gunshots sound, and Kat screams in pain.

• Berant Zhu as Jim
• Regina Lei as Kat
• Tzu-Chiang Wang [zh] as the Businessman
• Emerson Tsai as Warren Liu
• Wei-Hua Lan as Alan Wong
• Ralf Chiu as Mr. Lin
• Lue-Keng Huang as Kevin
• Ying-Ru Chen as Molly
• Flamey as Extra #1

The Sadness was shot on Red Digital Cinema "Monstro" cameras with Arri "Signature Prime" lenses. Filming lasted 28 days in Keelung and Taipei.^[7] The film's special effects were handled by IF SFX Art Maker.^[5][7] The effects crew spent up to three months producing a number of practical artificial heads, including some that could be made to explode or spray blood, as well as prostheses, organs, and other props.^[5] Production designer Liu Chin-Fu oversaw the film's set design, which included a subway car and a hospital.^{[citation needed]}

The Sadness was released in Taiwan on 22 January 2021.^[5] It had its international premiere at the 74th Locarno International Film Festival in Switzerland on 12 August 2021.^[6] It was screened at the 25th Fantasia International Film Festival in Canada in August 2021,^[6][8] as well as at Fantastic Fest in the U.S. in September 2021.^[4]

Raven Banner Entertainment acquired the worldwide distribution rights to the film.^[9] In April 2022, it was confirmed that the film would begin streaming on Shudder on May 12, 2022.^{[citation needed]}